Re: [dpdk-dev] [PATCH] examples/ipsec-secgw: Update checksum while decrementing ttl

["De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>]

> -----Original Message-----
> From: Akhil Goyal [mailto:akhil.goyal@nxp.com]
> Sent: Wednesday, October 19, 2016 1:38 AM
> To: De Lara Guarch, Pablo; Gonzalez Monroy, Sergio; dev@dpdk.org
> Subject: RE: [PATCH] examples/ipsec-secgw: Update checksum while
> decrementing ttl
> 
> 
> 
> -----Original Message-----
> From: De Lara Guarch, Pablo [mailto:pablo.de.lara.guarch@intel.com]
> Sent: Monday, October 17, 2016 10:35 PM
> To: Gonzalez Monroy, Sergio <sergio.gonzalez.monroy@intel.com>; Akhil
> Goyal <akhil.goyal@nxp.com>; dev@dpdk.org
> Subject: RE: [PATCH] examples/ipsec-secgw: Update checksum while
> decrementing ttl
> 
> 
> 
> > -----Original Message-----
> > From: Gonzalez Monroy, Sergio
> > Sent: Monday, October 10, 2016 5:05 AM
> > To: De Lara Guarch, Pablo; Akhil Goyal; dev@dpdk.org
> > Subject: Re: [PATCH] examples/ipsec-secgw: Update checksum while
> > decrementing ttl
> >
> > On 07/10/2016 21:53, De Lara Guarch, Pablo wrote:
> > >> -----Original Message-----
> > >> From: Akhil Goyal [mailto:akhil.goyal@nxp.com]
> > >> Sent: Tuesday, October 04, 2016 11:33 PM
> > >> To: De Lara Guarch, Pablo; Gonzalez Monroy, Sergio; dev@dpdk.org
> > >> Subject: Re: [PATCH] examples/ipsec-secgw: Update checksum while
> > >> decrementing ttl
> > >>
> > >> On 10/5/2016 6:04 AM, De Lara Guarch, Pablo wrote:
> > >>>
> > >>>> -----Original Message-----
> > >>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Sergio
> > Gonzalez
> > >>>> Monroy
> > >>>> Sent: Monday, September 26, 2016 6:28 AM
> > >>>> To: akhil.goyal@nxp.com; dev@dpdk.org
> > >>>> Subject: Re: [dpdk-dev] [PATCH] examples/ipsec-secgw: Update
> > checksum
> > >>>> while decrementing ttl
> > >>>>
> > >>>> Hi Akhil,
> > >>>>
> > >>>> This application relies on checksum offload in both outbound and
> > >> inbound
> > >>>> paths (PKT_TX_IP_CKSUM flag).
> > >> [Akhil]Agreed that the application relies on checksum offload, but
> > >> here we are talking about the inner ip header. Inner IP checksum
> > >> will be updated on the next end point after decryption. This would
> > >> expect that the next end point must have checksum offload
> > >> capability. What if we are capturing the encrypted packets on
> > >> wireshark or say send it to some other machine which does not run
> > >> DPDK and do not know about
> > checksum
> > >> offload, then wireshark/other machine will not be able to get the
> > >> correct the checksum and will show error.
> >
> > Understood, we need to have a valid inner checksum.
> > RFC1624 states that the computation would be incorrect in
> > corner/boundary case.
> > I reckon you are basing your incremental update on RFC1141?
> >
> > Also I think you should take care of endianess and increment the
> > checksum with
> > host_to_be(0x0100) instead of +1.
> >
> > >>>> Because we assume that we always forward the packet in both
> > >>>> paths,
> > we
> > >>>> decrement the ttl in both inbound and outbound.
> > >>>> You seem to only increment (recalculate) the checksum of the
> > >>>> inner IP header in the outbound path but not the inbound path.
> > >> [Akhil]Correct I missed out the inbound path.
> > >>>> Also, in the inbound path you have to consider a possible ECN
> > >>>> value
> > >> update.
> > >> [Akhil]If I take care of the ECN then it would mean I need to
> > >> calculate the checksum completely, incremental checksum wont give
> correct results.
> > >> This would surely impact performance. Any suggestion on how should
> > >> we take care of ECN update. Should I recalculate the checksum and
> > >> send the patch for ECN update? Or do we have a better solution.
> >
> > If I am understanding the RFCs mentioned above correctly, you should
> > be able to do incremental checksum update for any 16bit field/value of
> > the IP header.
> > I don't see no reason why you couldn't do something like that, except
> > that you would have to follow the full equation instead of just adding
> > 0x0100, which would be always the case when decrementing TTL.
> >
> > What do you think?
> 
> Any comments, Akhil?
> 
> Ok.. will send next version soon.

Hi Akhil,
Are you sending that version soon? It won't make it the RC2, but it may be merged for RC3.

Thanks,
Pablo